In automation systems individual peripheral modules or peripheral assemblies are frequently merged to form so-called load groups. Such load groups are supplied with a supply voltage via a power supply unit. The formation of load groups which can be individually and specifically switched off and on enables a high degree of flexibility when connecting various users within the automation system. Moreover, with the formation of several load groups independently supplied with a supply voltage a diagnosis can be performed more easily in the event of a fault. In addition, the formation of load groups which can be specifically switched off in the context of a fault ensures the most efficient implementation possible, for example of an EMERGENCY-OFF function.
As a rule, so-called power modules or supply modules are available for selective load group formation. These power modules supply several peripheral modules or assemblies with the required supply voltage, which is 24 V as standard in the context of an automation system. The power modules and the respective peripheral modules connected to them, which form a common load group, are inserted into consecutive slots within the rack. A power module together with the subsequent peripheral modules forms a potential group independent of the other groups. As a rule, self-constructing internal voltage buses are used for individual load group formation within the modular peripheral systems. The voltage buses serve to supply voltage to the peripheral modules belonging to a load group. The power module also ensures that the voltage bus of the previous load group is disconnected from the voltage bus of the following load group and that the following load group only receives its supply voltage via the power module. However, power modules which ensure a power supply must be again and again inserted between the various peripheral assemblies which are connected with data technology via their connections to the different users of the automation system, and which therefore fulfill the actual automation tasks. On the one hand, slots are required on the rack, and on the other hand, when planning the automation system the number of peripheral modules which are to form a load group should be considered from the outset. In a subsequent reconfiguration of the system it may then be necessary to remove the individual peripheral assemblies from the rack and rearrange them so that a newly required supply module can be inserted between them.